The present invention relates to a form of solid waste material shredding and comminuting apparatus. Comminution, or the reduction of particle size of solid waste material to small or minute particles, is preformed by shearing, shredding and crushing and the like of the waste material. Such comminution is commonly performed by feeding solid waste material into the interface of counter-rotating intermeshing cutter members. Shearing action may occur when particles of waste material are cut or crushed by the "scissors" action between cutters on one shaft and those on the other shaft due to overlap of root diameters of the cutters. The particles may also be shredded by the tearing action of the leading edge of a cutting element against solid material trapped between cutting elements of the opposite stack.
In the prior art of such comminution apparatus there is provided a pair of rotating shafts with their axes of rotation parallel to one another, with sets or stacks of individual cutter disks and spacers fixedly mounted on each shaft, and mutually intermeshing. The spacers are to maintain a fixed separation between the teeth of the cutter disks. When such apparatus is operated over a long period of time, the individual cutter disks and/or the shredding teeth thereof may become dislodged, distorted broken-off or slip in rotation along the axis of the shaft owing to the fact that such cutter disks and teeth are subject to large shear, shock, bending and torsion forces which must be borne or carried solely by an individual disk or tooth. Stated differently, there is no opportunity for sharing or distribution of such forces among the various adjacent disks, teeth or spacers along the axis of the shaft. Consequently, such prior art devices are subject to many undesireable drawbacks and disadvantages, which may be observed as, for example, in the accummulation of waste material between the cutter members, failure of one or more of the cutter disks to rotate, misalignment of the cutter teeth, anyone or all of these may produce reduced comminution efficiency and reliability and the like.
Apparatus of the type to which the present invention relates, are known and described in the prior art, for example, such as U.S. Pat. No. 4,046,324, to Joseph W. Chambers, issued Sept. 6, 1977, entitled "Solid Waste Comminution". This device has two interacting stacks of shredding members mounted on substantially parallel shafts and are positioned in transverse arrangement with respect to the direction of the waste material is introduced into the comminutor apparatus. A shredding disk of each stack interacts with a shredding member on the other stack, whereby the individual cutter members cooperatively interact in pairs within the comminutor. Teeth are provided on at least one member of each pair of shredding members for cutting during rotation thereof. The primary novelty of this prior art apparatus appears to reside in the existence of cutter disks having shredding members or teeth for cutting in both directions of shaft rotation and the ability of the shafts to be driven in either direction, whereby the device cuts in both directions.
In another U.S. Pat. No. 4,690,340, to Takefumi Hatanaka, issued Sept. 1, 1987, entitled "Waste Material Shredder", there is disclosed an apparatus having a pair of counter-rotating cutter rollers with mutually meshing individual cutter disks mounted thereon and fixed individual spacer members separating the cutter disks. This device is directed toward eliminating jamming of the shredder due to the build-up of chips during the shredding of sheets of waste material between the spacers. Jamming of the device is said to be eliminated by a special configuration of the cutter disks, with chip clearance protrusions being formed between the peripheral teeth which act to remove such chips, thereby overcomming a problem with prior art "cross-cut" type shredders.
In other U.S. Pat. Nos., Ser. No. 4,565,330, to Hiroharu Katoh, issued Jan. 21, 1986, entitled "Shredding Apparatus", and entitled "Apparatus for Shredding Rubber Tires", each also discloses cutter disks with separating spacer disks disposed on substantially parallel twin shafts which are rotatable in opposing directions in intermeshing relationship.
Each of the above cited patented apparatus and other prior art patents not cited utilize as the novelty the individual cutter and spacer disk arrangements for their operation. Various protruding teeth configurations, multiple teeth on the disk, differences in root diameters of the cutter teeth and spacers and the like are utilized to accommodate a wide variety of waste materials to enhance the efficiency and reliability of such prior art devices. However, none of the known prior art devices solves the long standing and continued problems of poor efficiency shredding, sizing, jamming, distortion, broken teeth or dislodgement of cutter disks or teeth when such arrangements are utilized. Thus, it appears that the most common technique in the prior art is to use alternate stacking of cutters and spacer disks on shafts to provide an arrangement for the shredder inter-meshing or inter-action have not realized or appreciated the need to provide an arrangement which is strong and durable and which is capable of distributing the stresses encounted therein along the axial length of the apparatus rather than having it concentrated on the individual cutter and disk members.
In U.S. Pat. Nos., Serial No. 3,664,592, to Luitpold Schweigert, issued May 23, 1972, "entitled Machine for Granulating Bulk Rubbish or Bulky Refuse of any Kind ", there is disclosed a machine for comminuting bulky refuse. The machine includes a pair of parallel rotary shafts, which have distributed therealong a plurality of rotary cutters and affixed thereto for rotation therewith, with cutters being spaced apart from each other along the shaft and with each cutter having a single tooth and the teeth of the cutters distributed along each shaft being angularly staggered about the axis of each shaft consistent with prior art practices.
The cutters on one shaft are aligned with the spaces between the cutters on the other shaft while each cutter has a circular portion fixed to the shaft and the single tooth of each cutter projects beyond the circular portion of each cutter. The single cutting tooth on the several cutters of one shaft move through the spaces between the circular portions of the cutter on the other shaft. The rotary shafts with the cutters thereon are housed within a trough-shaped housing carrying an upper inlet through which material is supplied to the cutters, this housing having a lower outlet situated beneath the rotary cutters at a location adjacent to the space through which the teeth of the cutters turn during rotation of the shafts. This lower outlet of the housing carries a structure which prevents the comminuted material from passing through the outlet until this material has been reduced to a given size, and the cutting teeth function not only to comminute the material, but also to repeatedly act on the material until it has been reduced to the size required to pass beyond the outlet.